Such illumination systems are known per se. They are used, inter alia, as luminaires for general lighting purposes, for example, for office lighting or shop lighting, for example, shop-window lighting or lighting of (transparent or semi-transparent) plates of glass or of (transparent) synthetic resin on which, for example, jewelry is displayed. An alternative application is the use of such systems for illuminating billboards.
Such known illumination systems are also used as backlight-emitting panels in (picture) display devices, for example, for TV sets and monitors. These systems are particularly suitable for use as backlights for non-emissive displays such as liquid crystal display devices, also referred to as LCD panels, which are used in (portable) computers or (portable) telephones.
These display devices usually comprise a substrate provided with a regular pattern of pixels, each of which is controlled by at least one electrode. The display device utilizes a control circuit for achieving a picture or a data-graphical display in a relevant field of a (picture) screen of the (picture) display device. The light originating from the backlight in an LCD device is modulated by means of a switch or modulator, using various types of liquid crystal effects. In addition, the display may be based on electrophoretic or electromechanical effects.
The illumination system mentioned in the opening paragraph comprises a light-emitting diode (further also referred to as LED). This LED may be provided in the vicinity of or tangent to a light-transmitting edge surface of the light-emitting panel, in which case light originating from the light source is incident on the light-transmitting edge surface during operation and distributes itself in the panel. Alternatively, the illumination system comprises a plurality of LEDs, which may be distributed on the rear wall of the light-transmitting panel.
Such a system for illuminating an image display device is known from U.S. patent application US 2004/0130515. The illumination system comprises a plurality of LEDs and a light guide plate. The LEDs are arranged for direct illumination of the image display device in a regular array. The light guide plate is arranged between the regular array of LEDs and the image display device and has a plurality of recesses, each recess comprising a LED from the plurality of LEDs. The known illumination system has the disadvantage that the light-emitting window has a relatively poor uniformity throughout.